It was good police work, with help from federal law enforcement agencies. Aside from the security video, there were undercover buys, which led to the large cache of explosives and ultimately to the arrests of the two men police say were the masterminds of the operation.
Marc Ormando and Sean Gunther were arrested March 6. Police say they were involved in making and selling explosives. Large quantities were found at Ormando's home in Pacifica.
"We believe it could have leveled the house. It could have taken down neighbors' houses," said Sgt. Rachel Murphy from the San Francisco Police Special Investigations Division.
Police told ABC7News, they seized nine drums containing more than 400 pounds of explosive powder. They found even more powder stuffed in 40 smaller containers. There were powerful rockets and 700 barrel bombs in varying sizes. And that's not all.
"We had miscellaneous commercial grade fireworks and there was over 1,300 pounds of these seized as well," said Murphy.
Police also confiscated a cache of weapons -- nine handguns and eight rifles. Police began their investigation into the bomb making operation four months ago. It started when Ryan Schultz, an employee of Centerfolds nightclub, was arrested and charged with igniting an explosive device on Broadway.
ABC7 News obtained the security video which shows what happened the night of Nov. 13. Police say Schultz is the man seen in the video placing the device on a metal pipe. He does it while people are still walking by. The bomb does not go off for several minutes, perhaps because of an ignition delay with the bomb's wick. All the time, people are still walking dangerously close. Then suddenly, the device explodes and it's amazing no one was hurt.
"When it explodes, there are pieces from the building, possibly from the pipe, that get sent out like shrapnel and if that hit somebody that could really hurt you," said Murphy.
The security video enabled police to identify Schultz. That led to Sean Gunther, who investigators say sold him explosives. They arrested Gunther at his San Pablo home and then Marc Ormando at his house in Pacifica.
There were so many explosive materials that police have had to keep them in three separate storage facilities. All three suspects have pleaded not guilty to the charges.